1. Field of the Invention
The present invention relates to a continuously variable transmission for a vehicle.
2. Description of the Related Art
As a continuously variable transmission for a vehicle, a transmission capable of changing a speed ratio to a very low speed range has been proposed. As such a continuously variable transmission, Japanese Patent Laid-Open No. 2003-194204 discloses a continuously variable transmission that combines a toroidal type continuously variable transmission mechanism and a planetary gear mechanism. The continuously variable transmission of Japanese Patent Laid-Open No. 2003-194204 has a mode in which a driving force is input to the planetary gear mechanism through the continuously variable transmission mechanism, and also input to the planetary gear mechanism without an intervention of the continuously variable transmission mechanism as well, thereby differentially operating the planetary gear mechanism. In this mode, conversion between normal rotation and reverse rotation of the output shaft can be performed around a state (geared neutral: GN) in which rotation of the output shaft is stopped by adjusting the speed ratio of the continuously variable transmission mechanism.
To control the speed ratio of the continuously variable transmission mechanism, vehicle speed information is necessary. As a sensor used to detect the vehicle speed, for example, a pulse sensor such as a magnetic pickup sensor that detects the rotation speed of the output shaft of the continuously variable transmission is known. In the range of very low speed (very low rotation speed) before and after GN, however, the pulse sensor may be unable to correctly detect the rotation speed, and it may be difficult to set the speed ratio according to the vehicle speed. A sensor having a higher detection accuracy may be used. However, this leads to an increase in cost.